Gut Bacteria Build Weapons from Viruses

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Bacteria in the gut can unexpectedly manufacture viruses to kill
off rivals during intestinal shootouts of sorts, researchers have
found.

These findings could help lead to new ways to kill off dangerous
germs, scientists added.

The average human gut is home to trillions of bacteria that
outnumber human cells in the body by a factor of 10 to 1. Often
these bacteria are helpful, aiding in digestion and synthesis of
key vitamins.

Many bacteria in the digestive tract are infected with and churn
out viruses known as
bacteriophages, or phages for short. Bacteriophages only
target and destroy bacteria — researchers have investigated them
for nearly a century as an alternate way to fight bacterial
infections.

"The
gut microbiota harbors a teeming universe of phages,"
researcher Lora Hooper, a microbiologist at the University of
Texas Southwestern Medical Center in Dallas, told LiveScience.
"However, nothing was known about whether these phages were
benefiting their bacterial hosts, whether they were predators, or
anything about their role in the larger context of the gut
ecosystem." [ Tiny
& Nasty: Images of Things That Make Us Sick ]

Scientists focused on Enterococcus faecalis, a gut
microbe that can makes up nearly 1 percent of all bacteria in the
digestive tract and is a leading cause of antibiotic-resistant
hospital-acquired bacterial infections of the blood. Genetic
analysis of this species has revealed it comes in a highly
diverse range of strains.

Phages have woven their genomes directly into that of E.
faecalis. It takes extra energy for the bacterium to
manufacture these viruses, "suggesting that harboring the phage
must confer a significant advantage to the host bacteria," Hooper
said. "Otherwise we would not expect the host bacteria to
maintain the phage genomes."

Researcher Breck Duerkop noticed that E. faecalis
started producing more phages when he introduced it into
otherwise germ-free mice and let it grow in their intestines. "He
was curious about why this would be, and his curiosity led to the
findings," Hooper said.

The scientists discovered that one strain of E. faecalis
named V583 could generate phages that killed contending strains
in live mice.

"This phage confers benefit to its E. faecalis host by
acting as a weapon against other E. faecalis strains
that are competing for nutrients in the same intestinal niche,"
Hooper said.

Intriguingly, the phage weapon that a strain called V583 produces
is stitched together from two different phages — one gives
structure to the composite, while the other helps it infect
victims.

"This is one of the first examples of intraspecies
bacterial warfare in the intestinal ecosystem," Hooper added.
"Like many discoveries in science, this one was a complete
accident."

The researchers suspect the precursors of this phage colonized
V583 but failed to kill it. V583 then manufactured the phage,
using it to kill its rivals, which led both V583 and the phage to
flourish.

"One interesting question is whether there are other examples of
intraspecies shootouts going on in the intestine," Hooper said.
"We plan to look for bacteriophage in other bacterial species
that perform a similar function in defending the intestinal niche
of their host bacteria."

This research suggests that bacteriophages might eventually be
used to kill off dangerous
intestinal germs, "or otherwise might be used to shape the
intestinal bacterial community in a way that is more beneficial
for humans," Hooper said.

The scientists detailed their findings online today (Oct. 8) in
the journal Proceedings of the National Academy of Sciences.